1. Technical Field
This invention relates to thermally and electrically conductive caulking compounds and a process for making these compounds.
2. Background Art
Conductive caulks are made by incorporating thermally and/or electrically conductive fillers into a resin base material. Typically, these conductive fillers are uniformly sized particles. It has been found that the degree of thermal or electrical conductivity in these prior art caulks is dependent on the amount of filler that can be incorporated into the resin. Therefore, the packing factor of the filler material is of great importance. The more tightly the filler material can be packed in the resin, the higher the resulting conductivity. The theoretical maximum loading of prior art uniformly sized conductive particles into a resin base material would occur when each particle is surrounded by and in contact with as many other particles as their physical size will allow. FIG. 1 is exemplary of this maximum packing condition for uniformly sized particles 10 where the normally irregularly shaped particles are represented by spheres.
It has also been found that the thermal and electrical conductivity of a resin matrix caulk employing uniformly sized particles tends to change when flexed, or when the material expands due to external temperature increases. This change occurs because in both flexing and expanding the caulk, the filler particles are pulled apart, thereby reducing the contact between adjacent particles which is responsible of the high conductivity of the material.
Therefore, what is needed is a caulk having high thermal and electrical conductivity, and which substantially retains this conductivity when flexed or expanded.